(1)Field of the Invention
The present invention relates to an EDTV signal decoding apparatus which signal has a compatibility with a current NTSC signal and is transmitted by a letter box format multiplexed with video helper signals.
(2)Description of the Prior Art
Recently, according to spread of large screen television receivers, high definition pictures are absolutely required and EDTV (Enhanced Definition Television) system which executes a high picture quality processing at both transmitter side and receiver side has been studied.
A configuration of a decoding apparatus for a current EDTV signal (first generation EDTV, hereafter) is described in detail on pages 129-181 of a Clearvision Handbook published by Clearvision Spread Promotion Consulting Committee (Japan). A block diagram of an EDTV signal decoding apparatus for a first generation EDTV system in accordance with the prior art is shown in FIG. 1.
A composite video signal inputted from a composite video signal input terminal 40 is converted into a digital signal at an A/D converter 41 and is separated to a luminance signal Y and a chrominance signal C at a three dimensional adaptive type Y/C separator 15 according to a movement signal detected at a movement detector 14. The chrominance signal C is demodulated to an I signal and a Q signal at a color demodulator 32 and interpolating scanning lines are generated at a scanning line interpolator 42 for the luminance signal Y and the color signals I and Q. Then the horizontal scanning frequencies of the signals Y, I and Q are doubled at a double speed converter 43, the output signals of the double speed converter 43 are converted into analog signals at a D/A converter 44 and the luminance signal Y, the color signals I and Q are outputted from a luminance signal output terminal 45, an I signal output terminal 46 and a Q signal output terminal 47, respectively.
A second generation EDTV signal, however, is a video signal having a letter box format and a horizontal high frequency band helper signal (HH) is multiplexed with a video signal and an interpolating scanning line helper signal or a vertical high frequency band helper signal (VH) is multiplexed during upper/lower non-picture periods and displays a picture on a screen having a 16:9 aspect ratio by adding a second generation EDTV signal decoding apparatus to a video signal circuit. As a result, the number of circuit components and parts composing a second generation EDTV signal decoding apparatus is much larger than that of a first generation EDTV signal decoding apparatus and a circuit scale of the second generation EDTV signal decoding apparatus increases much more than that of the first generation EDTV signal decoding apparatus.